Effect of nitric oxide on responses of the human uterine arteries to vasopressin.

Nitric oxide (NO) is known to be an important relaxant of contractile activity in various muscles including the human uterine arteries. It has been suggested that NO plays a role in modulation of vascular action of arginin vasopressin (AVP), a strong vasoconstrictor of the human uterine arteries. Therefore, the purposes of this study were to investigate an involvement of endogenous NO in regulation of responses of the human intrauterine arteries to AVP and examine the effect of exogenous NO on contractions of the human intrauterine arteries evoked by AVP. Pretreatment of the artery rings with L-NA, an inhibitor of NO synthase significantly increased the resting force and enhanced the artery responses to AVP. The opposite effect has been observed after administration of 10(-6) mol/L sodium nitroprusside (SNP). Pretreatment of the artery rings with 10(-7) M CTX, a blocker of Ca(2+)-sensitive potassium channels with large conductance, did not change significantly their responses to AVP. Glibenclamide (1.5.10(-6) mol/L), a blocker of ATP-dependent potassium channels and apamin (10(-8) M), a specific blocker of Ca(2+)-sensitive potassium channels with small conductance strongly enhanced the maximum responses of the artery rings to AVP. Pretreatment with CTX significantly decreased the relaxation induced by SNP while apamin attenuated the sensitivity to SNP resulted in rightward shift of the concentration-response curve to SNP. In conclusion, this study indicates that: NO plays a role in regulation of both the vascular tone of the human intramyometrial arteries and their response to AVP. Ca(2+)-sensitive K(+) channels with small and large conductance are involved in the SNP-induced relaxation of these arteries. The pathways of this relaxation cannot be sufficiently explained at this moment and need further investigation.